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Thread: Bolt Life?

  1. #21
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    Quote Originally Posted by ABNAK View Post
    Okay whiz kids, could the AR still be an AR if the bolt had, say, four bigger and thicker lugs? The AK has two big ones, what would change if the AR had 4 stronger ones instead of 7? Obviously a matching barrel extension would be necessary, but is there something inherent in the AR15's design that would preclude fewer but stronger lugs?
    The degree of rotation to unlock would change, so the extension and carrier would need to be redesigned, at a minimum.
    Unless adopted by the military, I would think the cost of the system would keep sales low. Bolts are cheap. You’re talking $200 for every $6000 of ammo.

  2. #22
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    Considering that I might only put a few hundred rounds through each gun on a particular outing, and it's likely the gun will be cleaned and inspected afterward, the chances of a failure that will put the gun out of commission are practically zero. It's fascinating that we can chop off most of the lugs and the gun will still function.

  3. #23
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    Quote Originally Posted by ABNAK View Post
    Okay whiz kids, could the AR still be an AR if the bolt had, say, four bigger and thicker lugs? The AK has two big ones, what would change if the AR had 4 stronger ones instead of 7? Obviously a matching barrel extension would be necessary, but is there something inherent in the AR15's design that would preclude fewer but stronger lugs?
    It would take more rotation to unlock. I'm not an engineer, but it seems like it would take a steeper cam path and more force to get it turning. I've always heard that was a big part of the AR's secret sauce was the Johnson style bolt.

    Quote Originally Posted by lysander View Post
    14K to 15K is a long time in the military.

    Most non-infantry (a majority of the Army) unit probably go through 500 rounds per year, if that many, two qualification cycles. That's 28 years, almost forever.

    I'll wager that most M16A1s bought in the late 1960's still had original bolts and barrels when the M16A2 started to be fielded.

    A number of things could have caused the up swing in bolt consumption starting in 2000:

    1) a large number of M16s made prior to 1975 entered rework and had cracked bolts.
    2) the Army started shooting more.
    3) the ammunition pressure specifications increased (they did, BTW, in 1999 the M855 pressure limit went from 55,000 psi average/61,000 psi maximum to 58,700 psi/64,700 psi.)
    4) a combination of all of these.
    No, I mean in terms of round counts. I've heard of M16A1s that were rebarreled multiple times without replacing the bolts. Everything I've ever read or heard says that bolt life goes up exponentially with barrel and gas system length.

  4. #24
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    I thought Chris Bartocci had some information on this awhile back. Why the bolts were braking and what Colt did to fix the issue. And wasn't that about the time Karl Lewis developed the LMT Enhanced Bolt?
    The first 11 minutes discuss the issue.
    Last edited by prepare; 11-03-19 at 04:19.
    Big brother is watching and listing...

  5. #25
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    I am surprised nobody has brought up the KAC E3 bolt. The lugs have been re-designed to reduce the stress at the root. I have seen figures before and “heard” that the E3 has never experienced a broken lug (no evidence that I have seen/read).
    ETC (SW/AW), USN (1998-2008)
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    Quote Originally Posted by okie View Post
    No, I mean in terms of round counts. I've heard of M16A1s that were rebarreled multiple times without replacing the bolts. Everything I've ever read or heard says that bolt life goes up exponentially with barrel and gas system length.
    Exponentially? Never heard that much increase claimed.

    But yes, I was surprised to find that the bolt life for the M16 and M4 were pretty much the same.

  7. #27
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    Quote Originally Posted by prepare View Post
    I thought Chris Bartocci had some information on this awhile back. Why the bolts were braking and what Colt did to fix the issue. And wasn't that about the time Karl Lewis developed the LMT Enhanced Bolt?
    The first 11 minutes discuss the issue.
    At around 4:30, he mentioned bolts broken through the cam pin web.

    That is not mentioned as a failure mode in any of the reports I have for military M16 or M4s. And, some of these endurance tests go upwards of 15,000 rounds.

  8. #28
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    Quote Originally Posted by lysander View Post
    At around 4:30, he mentioned bolts broken through the cam pin web.

    That is not mentioned as a failure mode in any of the reports I have for military M16 or M4s. And, some of these endurance tests go upwards of 15,000 rounds.
    Around 2001-2002 it was definitely an issue in sand box. Heres another video that mentions it.
    Last edited by prepare; 11-03-19 at 12:41.
    Big brother is watching and listing...

  9. #29
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    Quote Originally Posted by alx01 View Post
    Probably the closest to redesign is an HK416 iteration.
    Not really. The form factor and design of the 416 bolt is basically identical to a traditional AR15 bolt in the locking lugs, extractor, and cam pin. The diameter is maintained as no gas rings are used, but that added diameter is in a non-critical area. The 416 has also suffered from cracked locking lugs. This was reportedly limited to a particular heat treat of a particular date code. A friend has sheared lugs from two separate personally owned 416 uppers (not mr556).
    SLG Defense 07/02 FFL/SOT

  10. #30
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    Quote Originally Posted by hotrodder636 View Post
    I am surprised nobody has brought up the KAC E3 bolt. The lugs have been re-designed to reduce the stress at the root. I have seen figures before and “heard” that the E3 has never experienced a broken lug (no evidence that I have seen/read).
    They are nice. Another interesting enhancement is the standard LMT bolt, which has an annular groove cut circumferentially around the bolt head at the base of the locking lugs. It acts to decrease the stress riser that results from (nearly) 90 degree cuts in this location in a traditional bolt.
    SLG Defense 07/02 FFL/SOT

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